The present invention relates to electroluminescent (EL) lamp modules and a method of making EL lamp modules. More particularly, an EL lamp module includes an EL lamp and a pre-printed circuit pattern that includes an EL driver and other electronic components that are printed and/or mechanically and electrically attached to the circuit pattern, by means of conductive and/or non-conductive pressure sensitive adhesives (PSA).
EL lamps are basically devices that convert electrical energy into light. AC current is passed between two electrodes insulated from each other and having a phosphorous material placed therebetween. Electrons in the phosphorous material are excited to a higher energy level by an electric field created between the two electrodes during the first quarter cycle of the AC voltage. During the second quarter cycle of the AC voltage, the applied field again approaches zero. This causes the electrons to return to their normal unexcited state. Excess energy is released in the form of light when these electrons return to their normal unexcited state. This process is repeated for the negative half of the AC cycle. Thus, light is emitted twice for each full cycle (Hz). Varying this frequency, as well as the applied AC voltage can control various properties of the emitted light. In general, the brightness of EL lamps increases with increased voltage and frequency.
EL lamps typically comprise numerous component layers. At the light-emitting side of an EL lamp (typically the top) is a front electrode, which is typically made of a transparent, conductive indium tin oxide (ITO) or antimony oxide (ATO) layer. A silver bus bar may be provided on top of a transparent or translucent electrode layer to deliver maximum and uniform current to the transparent or translucent electrode layer. Below the ITO or ATO and bus bar layers is a layer of phosphor, followed by a dielectric insulating layer and a rear lamp electrode layer. In some EL lamps, the ITO layer is sputtered on a polyester film, which acts as a flexible substrate. With a sputtered film, the transparent or translucent electrode becomes the base and the lamp can be built in the reverse order by printing the phosphor, barium and silver in that order. A relatively thick polyester film, typically four or more mils thick, is preferred because the rigidity and temperature stability that is required for screen-printing and for drying of the layers. The EL lamp construction may also include a top film laminate or coating to protect the component layers of the EL lamp construction.
The component structural layers of an EL lamp can be made from a variety of materials. Layers are normally printed by means of a flat bed screen method and are then batch dried, except for the base substrate and top film laminate. Some of the layers may be printed more than once in order to assure proper thickness and/or layer uniformity. For example, the dielectric material needs sufficient thickness to prevent continuous pinholes or voids, which may cause shorting between the electrodes. Multiple thin layers of the printed dielectric minimize the chances for a continuous pinhole through the dielectric, thus minimizing the chances of a shorted lamp. On the other hand, the dielectric layer is prone to cracking when multiple layers are printed one over the other. Thus, control over the printing process for the dielectric layer is extremely important. If the dielectric is too thick, the required operating voltage and/or frequency to achieve a given brightness will have to be increased. Also, the chances of cracking are increased when the dielectric layer becomes too thick. Thus, consistent dielectric thickness in production of EL lamps is important to ensure consistent lamp brightness across a given production run of lamps.
Operation of the EL lamp may include a power source and intervening circuitry, including such components as resistors, capacitors, diodes, inductors, inverters, and/or transformers, to function. The nominal voltage and frequency for the EL lamps described herein are typically about 100 Volts (AC) and 400 Hz. However, these EL lamps can be made for operation from approximately 65-200 Volts (AC) and 60-1000 Hz. The EL lamps can be operated directly from an AC power source or from a DC power source. If an AC power source is used directly, then a battery would not be required, nor would any other electrical components. An example of this is an EL night-light that is plugged directly to a standard house electrical system. However, if increased brightness is required, then additional electronics may be required to increase the electrical frequency of the current for the lamp. If a DC power source is used, such as small batteries, an inverter is required to convert the DC current to AC current. In larger applications, a resonating transformer inverter can be used. This typically consists of a transformer in conjunction with a transistor and resistors and capacitors. In smaller applications, such as placement on PC boards having minimal board component height constraints or for ornamental applications, an integrated circuit chip (IC) inverter can generally be used in conjunction with a diode, capacitors, resistors, inductor, and a switching arrangement.
Varying the frequency, as well as the applied AC voltage, can control various properties of the emitted light from the EL lamp. For example, the brightness in general of the EL lamp increases with increased voltage and frequency. Additionally, the color produced is greatly influenced by the lamp frequency. Unfortunately, when the operating voltage and/or frequency of an EL lamp are increased, the life of the EL lamp may decrease more rapidly. EL lamp life is often defined as the point in which the light output reaches 50% of the original output. Therefore, in addition to various other design constraints, these properties must be balanced against the desired product life of the EL lamp module to determine the proper operating voltage and/or frequency. In considering these variables, it is important to prevent voltage breakdown across the electrodes of the EL lamp, which results in lamp malfunction or failure.
EL lamps in general, and flexible EL lamps in particular, should be constructed for easy and reliable installation in the end product or application. In installation, the EL lamp must be attached mechanically and electrically in the application. Prior art EL lamps treat the mechanical installation and the electrical installation separately. The EL lamp manufacturer produces and supplies the lamp component separately from the power source and any intervening electrical components necessary for the proper operation of the EL lamp device. The manufacturer of the final part or device, or some intermediate manufacturer, then assembles or connects the lamp, circuitry and power source for the final application generally by hard connections and wiring. The conventional EL lamp driver is produced on a PCB (printed circuit board) using conventional methods, such as soldering, to attach the necessary electrical components. The power leads and driver circuit could be either a copper etched board or hard wire depending on the device and desired configuration. This increases manufacturing cycle times and increases the probability of the occurrence of manufacturing defects by utilizing separate electrical and mechanical connections in the EL lamp design.
It is therefore an object of the present invention to provide an EL lamp module and a method of producing an EL lamp module that has superior performance and is cost effective to produce.
These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.